1. Field of the Invention
The present invention relates to an etching apparatus for a liquid crystal display device, and more particularly, to an etching apparatus enabling to increase productivity by sensing a level of an etchant using a contact sensor and preventing the sensor from being degraded by particles.
2. Discussion of the Related Art
Recently, many efforts have been made to research and develop various flat display panels such as LCD (liquid crystal display), PDP (plasma display panel), ELD (electroluminescent display), VFD (vacuum fluorescent display), and the like. LCD is practically used because of the characteristics or advantages of high quality image and low power consumption.
The liquid crystal display device includes lower and upper substrates confronting each other to leave a predetermined interval from each other and a liquid crystal layer formed between the substrates. A black matrix and a color filter layer are formed on the upper substrate. And, on the lower substrate formed are a plurality of gate and data lines arranged horizontally and vertically with a predetermined interval from each other to define pixel areas and thin film transistors and pixel electrodes formed in the pixel areas, respectively.
Lightweight and compact size are demanded for the liquid crystal display device to be applied to portable TV set, notebook computer, and the like. Yet, the structure or technology of the liquid crystal display device has limitation for the lightweight and compact size. However, the glass substrate as a basic element of the liquid crystal display device is the heaviest in the components of the liquid crystal display device. Hence, many efforts are made to reduce the weight of the glass substrate.
In order to reduce the weight of the glass substrate, a thickness of the glass substrate should be decreased. Yet, a physical force is occasionally applied to the glass substrate in the process of fabricating the liquid crystal display device. And, the glass substrate undergoes a number of heating and cooling processes. Hence, the thin glass becomes easy to be broken. Recently, used is a new method including the steps of using a thick glass substrate in the early stage of process and thinning the glass substrate in the later process. Namely, devices and color filters are formed on thick glass substrates to prepare upper and lower glass substrates, the upper and lower glass substrates are bonded to each other, and then outer surfaces of the glass substrates are etched to reduce an overall thickness of the liquid crystal display device.
Generally, the glass substrate is etched by wet etching carried out in a manner that the glass substrate is dipped in a bath filled with an etchant of strong acid etching a surface of the glass substrate.
However, such a method of wet etching makes the uneven surface of the substrate since particles generated from the etching process sticks to the substrate. Moreover, if the supply of the etchant fails to be controlled, the glass substrate is etched in part to generate the failure caused by the difference between the etched and non-etched portions.
In order to overcome such problems, a supply flow of an etchant is controlled using an etching apparatus equipped with a sensor enabling to sense the supply flow of the etchant.
An etching apparatus according to a related art is explained by referring to the attached drawings as follows.
FIG. 1 illustrates a schematic cross-sectional view of an etching apparatus according to a related art.
Referring to FIG. 1, an etching apparatus according to a related art includes an etching bath 1 having an etchant, a bubble plate 3 installed at a lower side inside the etching bath 1 to generate bubbles by a gas or an air supplied from outside to remove particles on a surface of a substrate which is being etched, a porous plate 5 installed on the bubble plate 3 to support a glass substrate (not shown in the drawing) to be etched, a supply pipe 15 supplying the bubble plate 3 with the air or the gas (N2), a buffer tank 13 discharging and filtering the etchant used for etching from the etching bath 1 through an etchant discharging pipe 11 for temporary storage, a deionized water supply unit 17 supplying deionized water, an undiluted etchant supply unit 19 supplying an undiluted etchant, an etchant supply tank 9 supplied with the deionized water and the undiluted etchant by the deionized water and the undiluted etchant supply units 17 and 19 and mixing the supplied deionized water and crude etchant with each other to supply the etching bath 1 with the etchant having a predetermined concentration through an etchant supply pipe 7, and an etchant detecting sensor 21 installed at an upper side of an inner wall of the etching bath 1 to detect a level of the etchant supplied to the etching bath 1.
In this case, the etchant supply tank 9 mixes the etchant using the deionized water supplied by the deionized water supply unit 17 and the undiluted etchant (ex. HF) supplied by the undiluted etchant supply unit 19, or is supplied with the etchant, which is recycled after completion of etching, from the buffer tank 13, to make the etchant having the predetermined concentration to be sent to the etching bath 1.
A plurality of glass substrate (not shown in the drawing) that will be etched are stood straight on the porous plate 5 with a predetermined interval from each other, and are dipped in the etchant filling the etching bath 1 for etching. Bubbles are generated through the bubble plate 3 and the etchant circulates uniformly by the bubbles. Thus, the glass substrates can be etched evenly. And, the bubbles detach the particles caused by the etching process from surfaces of the substrates.
Moreover, a guard 2 is formed on the inner wall of the etching bath 1 to protect the etchant detect sensor 21, and has a structure that front and rear sides in the drawing are open. If the etchant is supplied over a predetermined level, the etchant is put inside the guard 2.
In this case, when the etchant supplied from the etchant supply tank 9 to the etching bath 1 is supplied to the amount that the glass substrates are dipped in the etchant in part, the glass substrates fail to be etched uniformly but the portions of the glass substrates dipped in the etchant are etched only, whereby etch failure occurs. Hence, the etchant should be supplied to the level enabling to have the glass substrates dipped in the etchant entirely.
Therefore, it is able to control the supply of the etchant to the etching bath 1 stably using the etchant detect sensor 21 installed at the upper inner wall of the etching bath 1 before the etch is carried out. Moreover, it is also able to check the discharged state when the etchant is drained from the etching bath 1 after the completion of the etch.
Namely, the etchant detect sensor 21 according to the related art is a level sensor using an air pressure difference according to height of the etchant and the nitrogen gas (N2) supplied regularly and includes, as shown in FIG. 2, a magnetic valve 22 controlling a supply of a nitrogen gas for constant pressures of three tubes by receiving a nitrogen gas (N2) of low pressure from a portion of the air supply pipe (‘15’ in FIG. 1), a plurality of nitrogen pressure difference sensors 23a, 23b, and 23c detecting a pressure difference of the nitrogen gas cut off by an etchant 25 supplied inside an etching bath by having the nitrogen gas flow, and “L(low)”, “H(high)”, and “HH(high high)” nitrogen tubes 24a, 24b, and 24c receiving the nitrogen gas at low pressure to discharge the nitrogen gas in accordance with height.
Operation of the above-constituted nitrogen pressure difference sensor is explained in detail as follows.
First of all, when the etchant 25 is supplied inside the etching bath 1 for etching the glass substrate, the etching apparatus according to the related art detects that the nitrogen gas fails to be discharged since the “L” nitrogen tube 24a of the etchant detect sensor is blocked by the etchant having been supplied over a predetermined level, thereby recognizing that the etchant is being supplied inside the etching bath 1. The etching apparatus keeps supplying the etchant even if the nitrogen gas is unable to be discharged due to the blocked “L” nitrogen tube 24a, and detects that the etching bath 1 is full of the etchant since the nitrogen gas is discharged no more due to the blocked “HH” nitrogen tube 24c, thereby stopping the supply of the etchant.
Subsequently, the nitrogen gas is put in the bubble plate 3 from the air supply pipe 15 to generate bubbles, whereby an etching process of the glass substrates is carried out normally.
In this case, the guard 2 protects the etchant detect sensor 21 from the bubbles generated from the etchant, whereby the etchant maintains a horizontal level. The etching process is performed normally when the nitrogen gas is discharged through the “HH” or “H”nitrogen tubes 24c or 24b. Yet, etching failure may occur when the nitrogen gas is discharged through the “L” nitrogen tube 24a. 
Finally, when the etchant 25 is drained from the etching bath 1 after the completion of etching the glass substrate, the level of the etchant is lowered. Hence, the etching apparatus according to the related art recognizes that the etchant is normally drained since the nitrogen gas is discharged through the “L(low)”, “H(high)”, and “HH(high high)” nitrogen tubes 24a, 24b, and 24c, in order.
Unfortunately, the etching apparatus according to the related art has the following problems or disadvantages.
First of all, as the etching process is repeated, sludge as precipitates of the glass etched by the etchant blocks at least one of the “L”, “H”, and “HH” nitrogen tubes of the etchant detect sensor to perform the supply and discharge of the etchant abnormally. Hence, the etching apparatus according to the related art can cause failure of the etching process.
Secondly, when the “L” nitrogen tube is blocked, as shown at 26 in FIG. 2, a cleaning process for cleaning the glass substrate with deionized water is carried out under the circumstance that the drain of the etchant is not completed. Hence, the etching apparatus according to the related art causes degradation of the cleaning work since the deionized water as the cleaning material is mingled with the etchant.
Finally, the etching apparatus according to the related art consumes cost and time for replacement of the components or periodical cleaning works to prevent outlets of the “L”, “H”, and “HH” nitrogen tubes from being blocked by the sludge, thereby reducing productivity.